The present invention relates to a semiconductor device for mounting a spherical shaped semiconductor on a substrate. Further, it relates to a method of mounting the spherical shaped semiconductor on the substrate. More specifically, it relates to an alignment technique for aligning the spherical semiconductor with the substrate.
In the manufacturing of a semiconductor device, various semiconductor elements have conventionally been formed on the surface of a wafer-shaped semiconductor substrate. In contrast, Ball Semiconductor, Inc has disclosed, in xe2x80x9cNikkei Micro Devicexe2x80x9d issued on Jul. 1, 1998 and U.S. Pat. No. 5,877,943, etc., a technique for manufacturing a semiconductor device by using a spherical shaped semiconductor in which a semiconductor element is formed on the surface of a spherical semiconductor material (silicon). This spherical semiconductor exhibits a higher area/volume ratio as compared with the wafer-shaped semiconductor substrate, so that it is advantageous in that a large surface area can be ensured with a little amount of semiconductor material. A spherical shaped semiconductor material can be obtained, for example, by melting a granular polycrystalline semiconductor material having a diameter of approximately 1 mm in an argon atmosphere at a temperature of 1000xc2x0 C. to 10000xc2x0 C. using inductively coupled plasma to convert it into a monocrystal semiconductor material.
On the surface of such a spherical semiconductor material, it is possible to form various semiconductor elements by using, for example, an exposure method as shown in FIG. 7. In this exposure method, light transmitted through a mask is reflected toward a spherical semiconductor material 10 by mirrors 31, 32, 33, etc. arranged so as to surround the spherical semiconductor material 10, whereby the surface of the semiconductor material 10 is collectively exposed. In the etching process and the film formation process, etching gas, material gas, etc. are caused to flow through a pipe, and also the spherical semiconductor material 10 is caused to flow through a pipe.
The spherical semiconductor with various semiconductor elements formed on the spherical semiconductor material 10 as described above is then mounted on a substrate 15 in a manner as shown, for example, in FIG. 8, to form a semiconductor device 1. In this semiconductor device 1, each of three spherical semiconductors 11 is electrically connected to the substrate 15, and two of the three spherical semiconductors 11 are electrically connected to each other.
The semiconductor device 1 using such spherical semiconductors 11 will be mounted on various apparatus in the near future. At present, however, a technique has not yet been established that enables the spherical semiconductors 11 to be mounted on the substrate 15. When forming a conventional semiconductor device, semiconductor elements are incorporated in a semiconductor substrate shaped in plane, so that electrical connection is effected by using contact pads formed on plane surface, whereas, in the case in which the spherical semiconductor 11 is used, it is necessary to effect electrical connection by using contact pads formed on the spherical surface.
In view of the above problem, it is an object of the present invention to provide a semiconductor device having reliable electrical connection between a spherical semiconductor and a substrate and a method of manufacturing the same.
A semiconductor device of the present invention includes a spherical semiconductor, semiconductor elements such as transistor or diode etc. formed thereon, and contact pads that are electrically connected with the semiconductor elements. The semiconductor device also includes a substrate, and terminals formed on the surface of the substrate in which the spherical semiconductor will be mounted. The contact pads and the terminals are electrically connected via a fixative member, such as a solder, a conductive adhesive or an adhesive, arranged between the spherical semiconductor and the substrate. A high wettability area is formed at or around a central area of the spherical semiconductor where the substrate is closest. Specifically, the high wettability area is arranged on a surface of the contact pad. In such case, a wettability of the contact pad is higher than a wettability of the semiconductor material around the contact pad. Further, the contact pads may be processed to enhance the wettability with the fixative member. In addition, it is also preferable that a recess be formed in the substrate, at an area where the spherical semiconductor is mounted. In this construction, the positioning and retention of the spherical semiconductor is effected in a condition in which the spherical semiconductor is received by the recess. Therefore, the spherical semiconductor may be reliably mounted at a predetermined position on the substrate.
Additionally, it may be preferable to form a second high wettability area on the substrate at or around a central area of the substrate where the spherical semiconductor is mounted. The second high wettability area exhibits a higher wettability with the fixative material than that of a peripheral area around the high wettability area. Typically, the substrate where spherical comprises a base that is made from an electric non-conductive material such as glass, glass-epoxy or polycarbonate, terminals and a wiring pattern connecting the terminals which are made from conductive material. Preferably, the second high wettability area is arranged on a surface of the terminal, such that wettability of the terminal is higher than a wettability of the electric non-conductive substrate.
The method of mounting a spherical semiconductor comprises arranging the spherical semiconductor on the substrate, melting the fixative member arranged between the spherical semiconductor and the substrate, then, solidifying fixative material. In this case, the contact pad exhibits higher wettability with the fixative member than the peripheral area around the contact pad. To arrange the fixative member therebetween, for example, a layer of the fixative material is first applied to the contact pad of the spherical semiconductor.
In the above method, when the fixative material is melted, with the spherical semiconductor being arranged on the layer of the fixative material, a force is felt by the spherical semiconductor due to the surface tension of the melted fixative material and the difference in wettability between the high wettability area of the spherical semiconductor and the peripheral area. This force causes the spherical semiconductor and the contact pad to be urged into alignment with the terminal of the substrate. Thus, even if the position or orientation of the spherical semiconductor is somewhat misaligned from this terminal, the positioning of the spherical semiconductor will self-align when the fixative material is melted. Therefore, it is possible to reliably mount the spherical semiconductor at a predetermined position on the substrate.
To manufacture the present semiconductor device, a method similar to the former method is used. That is, a method of mounting a spherical semiconductor comprises of arranging the spherical semiconductor on the substrate and melting the fixative member arranged between the spherical semiconductor and the substrate, and solidifying the fixative material. In this case, the terminal exhibits higher wettability with the fixative member than the peripheral area of the terminal. To arrange the fixative member therebetween, for example, a layer of the fixative member is first applied to a contact pad of the spherical semiconductor. Then the spherical semiconductor is mounted to the substrate.
According to one aspect of the present invention during the manufacturing of the semiconductor device, as the spherical semiconductor is brought into contact with the fixative member a force created by the surface tension of the fixative material and the difference in wettability between the high wettability area of the spherical semiconductor and the peripheral area causes the spherical semiconductor and the contact pad to be urged into alignment with the terminal of the substrate. Thus, even if the position or orientation of the spherical semiconductor is somewhat deviated, such that the contact pads are not aligned with the terminal of the substrates, the positioning of the spherical semiconductor self aligns when the fixative member is melted. Therefore, it is possible to reliably mount the spherical semiconductor at a predetermined position on the substrate.
According to another aspect of the invention, the center of balance of the spherical semiconductor is set so as to direct the predetermined portion facing the substrate. In other words, the center of balance of the spherical semiconductor is arranged such that the predetermined portion is directed toward the terminals when it is arranged on the substrate. To change the center of balance to a certain position, the mass center of balance of the spherical semiconductor may be shifted by altering a density distribution of the wiring pattern and the contact pads formed on the surface of the spherical semiconductor. Alternatively, the center of balance of the spherical semiconductor may be shifted by varying a difference in the thickness of the layer of contact pad which is formed on the surface of the spherical semiconductor.
According to yet another aspect of the present invention, the substrate may include a recess in the area where the spherical semiconductor is mounted. With this embodiment, the spherical semiconductor may be reliably received and mounted in the recess area of the substrate. To manufacture such a semiconductor device constructed as described above, the spherical semiconductor may be positioned in the recess of the substrate, vibration imparted to the substrate so as to direct the contact pads into alignment with the terminal, and the spherical semiconductor and the substrate, coupled together with the fixative material.
In this embodiment, the center of balance of the spherical semiconductor is manipulated such that a predetermined part is aligned with the substrate terminals when it is arranged on the substrate, so that, even if the position or orientation not aligned with the terminal, the spherical semiconductor may move in the recess, in the predetermined direction according to the center of balance as vibrations are imparted to the substrate. Therefore, it is possible to mount the spherical semiconductor reliably at a predetermined position on the substrate.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.